FISHES OF CHESAPEAKE BAY 
147 
This fish is common only in restricted areas in the brackish and fresh-water arms and discon- 
nected pools and marshes of Chesapeake Bay, where, as a rule, the water is quiet and more or less 
stagnant. Although a few specimens of this fish have been reported as far north as New Jersey, 
the species may be said to reach the northern limits of its distribution in the Chesapeake region, 
where it is much more particular in the selection of its habitat than in more southern localities. 
However, it is usually quite common within the restricted places where it is found. 
This top minnow and closely related varieties or species are now widely employed in the 
South for the destruction of the aquatic stages of the mosquito. Gambusia are so effective for 
this purpose that it is doubtful if a more valuable fish swims in American waters. For accounts 
of the importance of this fish for the control of mosquito breeding see Hildebrand (1919, 1921, 
and 1925) and Howard (1920). 
Habitat— As here understood, the range of G. holbrooki extends from New Jersey to Florida. 
The top minnows of this genus that occur in the United States have been considered identical and 
as belonging to a single species by some writers while by others they are considered three distinct 
species. Geiser, from studies based upon the microscopic anatomy of the anal fin of the male, 
as already stated, has recently determined (1923, pp. 175 to 188) that the structure of the distal 
part of this fin (“gonopod”) is different in the eastern Gambusia from those of the South Central 
States, and he also found slight differences in this structure between specimens from the Central 
and Southwestern States; but he regards this last difference as of varietal importance only, while 
the more pronounced difference between the eastern and central specimens he regards as of spe- 
cific value. He also found the Mexican species, G. senilis, extending into Texas. According to 
Geiser, the species of Gambusia should now stand as follows: Eastern form, G. holbrooki; central 
form, G. affinis; southwestern form, G. affinis var. (unnamed, presumably palruelis Baird and 
Girard) ; and the Mexican form, G. senilis, from southern Texas. On the basis of these new divisions, 
the exact limits of distribution of the species and varieties remain to be established. (A further 
revision of the species of Gambusia and their distribution has appeared since the foregoing was 
written, in “Studies of the Fishes of the Order Cyprinodontes, VI,” by Carl L. Hubbs, in Miscel- 
laneous Publications No. 16, Museum of Zoology, University of Michigan, 1926, pp. 26-40, to which 
the reader is referred.) 
Chesapeake localities— {a) Previous records: “Lower Potomac” and St. Georges Island, (b) 
Specimens in collection: Annapolis, Love Point, Solomons, Oxford, and Crisfield, Md.; also from 
the marshes of Lynnhaven Bay, Va. 
Order SYNENTOGNATHI 
Family XXXIII.-BELONID/E. The needlefishes 
Body very elongate, slender, compressed or not; both jaws produced, forming a beak, the 
lower one a little the longer; maxillary united with the premaxillaries; each jaw with a band of 
short, pointed teeth and a series of enlarged ones; lateral line low, running along the edge of belly; 
scales small; dorsal fin opposite the anai; no finlets; air bladder present. 
KEY TO THE GENERA 
a. Body only moderately or not compressed, the depth not greatly exceeding the width 
Tylosurus, p. 147 
aa. Body rather strongly compressed, the width less than half the depth Ablennes, p. 150 
48. Genus TYLOSURUS Cocco. The needlefishes; the garfishes 
Body very elongate, little or not compressed; gill rakers obsolete; lateral line on sides of 
abdomen, becoming median on the caudal peduncle; dorsal and anal elevated anteriorly, falcate. 
